Various types of water jet power driven, aquatic vehicles have been devised and used. These vehicles are popular because of their speed, exceptional maneuverability, compact size, inexpensiveness, and appeal to all ages.
Water jet propelled boats are conventionally provided with a pump mounted within the craft. The pump is typically provided with an outlet near the stern of the boat for directing a jet of water rearwardly from the boat in order to propel the boat forwardly. The typical water inlet means for these pumps has been in the form of (1) scoops projecting below the planing surface of the boat hull and opening forwardly in order to enable the forward speed of the boat to assist in delivering the desired quantity of water to the pump; (2) forwardly opening recesses formed in the forward portions of the boat hull below the water line which enable the forward movement of the boat to assist in delivering the desired quantity of water to the water pump; and (3) openings in the bottom of the boat, usually one or two in number, which rely heavily upon the angle of attack of the bottom of the boat and the suction effected by the pump for delivering water to the pump.
The performance of these water jet propelled boats is limited by the means employed for converting the power output of the engine to thrust for propelling the water craft. Conventional propellers and pumps have been found to be inefficient due to cavitation losses, causing a great power loss. Cavitation occurs when vapor bubbles in a swiftly moving body of liquid impinge against a solid surface such as an impeller. The violent collapse of the vapor bubbles can blast particles of the metal out, causing the metal to develop a pitted or spongy appearance. In addition to causing the parts to become rapidly eroded, cavitation can also result in a drop in the performance of the jet pump by lowering efficiency and producing noise and vibrations.
However, conventional water jet pumps are typically difficult to disassemble for maintenance purposes. They are usually made of a heavy material, and the component parts are typically bolted together. As a result, it takes a long period of time to disassemble the pump assembly for maintenance or inspection purposes. In addition, the complexity of the connections is often too difficult for the ordinary consumer to master.
Further, conventional metal pumps tend to corrode and have a significant number of casting irregularities or rough surfaces which reduce efficiency. To improve efficiently, the owner of the watercraft often attempts to have this problem corrected by a process called "blueprinting", which results in additional cost and inconvenience.
Another problem with conventional jet pump powered water vehicles is the failure to entrain water during sharp cornering. This results in a crucial lack of motive force at the most steeply banked portion of a turn and lateral instability. This lack of continuous jet pump action during a turn contributes to a loss of control of the water vehicle and is a safety hazard. Proper water entrainment is essential to the operation of a jet pump throughout its entire performance range.
Conventional jet pumps used with small watercraft also typically do not feature a wear ring around the impeller. The absence of a wear ring results in the wear of the pump housing itself, so that the entire pump housing must be periodically replaced. This is an inconvenient and expensive proposition. Further, if a wear ring is provided, it is typically made of stainless steel and is not tapered. As a result, the wear ring is difficult to remove from the intake housing, so that it is difficult to reach the impeller for inspection and maintenance purposes.
Conventional jet pumps are also typically made from relatively heavy parts, and the additional weight requires more power from the engine. This problem is magnified when a jet pump is used with a small watercraft having a relatively small engine.
The present invention addresses the above problems associated with currently available jet pump assemblies.